Method for reducing myocardial infarct by application of intravascular hypothermia

ABSTRACT

Methods and apparatus for preventing myocardial infarction, or lessening the size/severity of an evolving myocardial infarction, by cooling at least the affected area of the myocardium using an intravascular heat exchange catheter. The heat exchange catheter may be inserted into the vasculature (e.g., a vein) and advanced to a position wherein a heat exchanger on the catheter is located in or near the heart (e.g., within the vena cava near the patient&#39;s heart). Thereafter, the heat exchange catheter is used to cool the myocardium (or the entire body of the patient) to a temperature that effectively lessens the metabolic rate and/or oxygen consumption of the ischemic myocardial cells or otherwise protects the ischemic myocardium from undergoing irreversible damage or infarction.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/933,979 filed Sep. 2, 2004 now U.S. Pat. No. 7,510,569, which is acontinuation of U.S. patent application Ser. No. 09/735,314 filed Dec.12, 2000 now U.S. Pat. No. 6,811,551, which claims priority to U.S.Provisional Patent Application Ser. No. 60/170,831 filed Dec. 14, 1999,the entire disclosure of each such application being expresslyincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to the field of cardiac therapy, andmore particularly to the intravascular application of hypothermia toprevent or reduce myocardial infarct resulting from myocardial ischemia.

BACKGROUND OF THE INVENTION

When the normal blood supply a person's heart muscle is disrupted, theperson may suffer what is commonly termed a heart attack. Heart attacksare one of the major health problems in the world. In the United Statesalone there are over 1.1 million heart attacks a year. Of those 1.1million victims, about 250,000 die within 1 hour. However, those thatsurvive the initial heart attack generally subsequently receivetreatment. In fact, about 375,000 of those heart attack victims willmake it to a hospital for treatment within 1 hour; about 637,000 willmake it to a hospital for treatment within 4 hours. Unfortunately, whentreated using current methods, heart attacks often result in serious andpermanent damage to the heart muscle. In fact, it is estimated thatabout 66% of the MI patients do not make a complete recovery, but rathersuffer permanent injury to cardiac muscle cells. An effective treatmentthat minimizes permanent damage to the heart as a result of the heartattack would be of great value to these patents.

In a typical heart attack, there is a blockage in an artery that provideblood to some of the cardiac muscle cells, so the cells in the affectedportion of the heart (termed the area at risk) experience ischemia, or alack of adequate blood flow. This ischemia results in an inadequatesupply of oxygen for the muscles and inadequate removal of waste productof muscle activity such as CO₂, lactic acid or other by-products ofmetabolism. These substances may therefore reach toxic concentrationsand thus, in turn, cause serious long-term consequences such as thebreakdown of the cell walls, release of toxic enzymes or the like, andultimately result in the death of many or all of the cardiac musclecells in the area at risk.

The ischemia, however, is not always permanent. In fact, if the heartattack does not result in the immediate death of the individual, theischemia is generally reversed either spontaneously or with medicalintervention. If the ischemia is a result of blockage of an artery by ablood clot, the clot may spontaneously dissolve in the ordinary courseof time due to the body's own natural thrombolytics, and blood may againflow to the affected area Alternatively, medical treatment may restoreblood flow. Such medical treatments include administration ofthrombolytic drugs, such as tPA, to dissolve blood clots in the vesselsof the heart to restore blood flow, balloon angioplasty, where aninterventional cardiologist steers a catheter with a balloon on the endinto the clogged artery and inflates the balloon to open the artery,coronary stenting, where an interventional cardiologist steers acatheter with a stent on it into the clogged vessel and expands thestent to place what amounts to a scaffold into the vessel with theblockage to hold the vessel open, or coronary by-pass surgery where ablood vessel is harvested from elsewhere in the patient's body and isattached around a blocked coronary artery to restore blood to theischemic tissue distal of the blockage. These treatments may be appliedindividually or in concert with one or more of the other treatments.

Generally if the ischemic event is for a short period of time oroxygenated blood is available to the affected tissue from another bloodsupply, for example from collateral arteries or even from blood withinthe heart cavity, some or all of the muscle cells in the area at riskmay survive and ultimately recover much or all of their function.However, if the period of ischemia is long enough and severe enough, thecardiac muscle cells in the area at risk may in fact die as a result ofthe ischemic insult. The area of dead tissue resulting from this celldeath is called an infarct and the area may be said to be infarcted.

Unlike many cells in the body, for example, skeletal muscle cells,cardiac muscle cells do not significantly regenerate. Thus an infarctedregion of cardiac muscle cells will generally be a permanentlynon-functioning portion of the patient's heart. This will result indecreased overall heart function, which may lead to systemic vascularinsufficiency, congestive heart failure, and even death. It is thus ofgreat importance to minimize the amount of infarct that results fromcardiac ischemic events.

Infarct may result from heart attacks as described above, and may alsoresult from myocardial ischemic events as the result of other causes andmay even be predicable. For example, in so-called beating heart by-passsurgery, the surgeon stops the heart for short periods of time to sewgrafts onto the surface of the heart. In such a procedure, the heart isdeprived of blood during the time that circulation is stopped, andunless protected, infarct can result from this ischemic event.

Another common interventional procedure, cardiac balloon angioplasty,also disrupts the blood supply to part of the heart and results inpredictable ischemia. In balloon angioplasty of the heart, aninterventional cardiologist inserts a balloon catheter into thevasculature of the heart with the balloon deflated. The balloon isplaced at a location where the interventionalist wants to dilate thevessel, and then inflates the balloon against the walls of the vessel.When the balloon is inflated, it fills the vessel in question and blocksmost if not all blood from flowing through that vessel. In this way, itcreates an area of ischemia downstream from the balloon, which ischemiapersists for as long as the balloon is inflated. Although attempts havebeen made to relieve this ischemia by means of catheters that allowperfusion from one side of the balloon to the other during inflation (socalled auto-perfusion balloons), these have generally proven to beinadequate.

It is also sometimes the case that during or after angioplasty thedilated vessel is either dissected or goes into spasm. If the vesselspasms shut or is dissected, the blood supply to all the tissuevascularized by the artery in question suffers severe ischemia andpotential infarct. In such cases the patient is generally taken to asurgical suite and open chest by-pass is performed. Until the by-pass issuccessfully completed, the area at risk remains starved of blood.

Medical practitioners have attempted to reduce the infarct resultingfrom the ischemic events suffered during beating heart surgery andangioplasty with drugs and through a technique known as preconditioning.Drugs, for example adenosine and RheothRx, have been tried, and althoughunder some circumstances they may have some effect, they have ultimatelyproven generally inadequate for one reason or another.

In preconditioning, the cardiac muscle is subjected to short periods ofischemia, for example two or three episodes of 5 minutes of ischemiafollowed by reperfusion, prior to the angioplasty or other anticipatedprocedure that will expose the heart to a more prolonged ischemic event.This has been found to reduce the infarct size resulting from theprolonged subsequent ischemia somewhat, but is difficult to performsafely, requires a complex set-up and is an invasive procedure.Importantly, precondition must occur well in advance of the ischemicevent. For all these reasons it is generally not a useful procedure, andbecause it necessarily must occur in advance of the anticipated ischemicevent, it is unsuitable for treating ischemia due to heart attacks thathave already occurred or are in process.

Under ordinary circumstances, the temperature of the body andparticularly that of the blood is maintained by the body'sthermoregulatory system at a very constant temperature of about 37° C.(98.6° F.) sometimes referred to as normothermia. The amount of heatgenerated by the body's metabolism is very precisely balanced by theamount of heat lost to the environment. The circulating blood serves tokeep the entire body and particularly the heart, at normothermia. Deephypothermia (30° C. or lower) has long been known to be neuroprotective,and believed to be cardioprotective as well. More recently, theadvantage of mild hypothermia (only as low as 32° C. or even as warm asbetween 35° C. and normothermia) to ischemic cardiac tissue has beenrecognized, either before and/or during an anticipated ischemic eventsuch as may occur in beating heart surgery or coronary angioplasty,during an ischemic event such as a heart attack in progress, or soonafter an ischemic event such as a heart attack that has alreadyoccurred. No satisfactory method of achieving this mild cardiachypothermia in the human clinical setting, however, has been availablebefore this invention. In rabbits, ice bags or ice-filled surgicalgloves have been applied directly to the heart in an open-chestprocedure. This method is clearly very invasive, clumsy and lackscontrol over the level of hypothermia applied. Other attempts have beenmade using cooling blankets or externally applied ice bags or icedblankets. These methods are slow, lack adequate control over the patienttemperature, are not directed to the heart muscle and therefore are noteffective in the human clinical setting to adequately reduce cardiactemperature, especially in obese patients.

Another method of achieving cardiac hypothermia has been proposed, thatof pericardial lavage using a two-lumen catheter, with the distal endsof both lumens (one input and one outflow) sealed inside the pericardialsack. A cold solution such as cold saline is circulated within thepericardial sack to cool the heart muscle. While this method is rapidand directed to the cardiac muscle, it is highly invasive, requiressurgical access to the pericardial sack which generally requires eitheran open chest procedure or a thoracotomy, involves piercing thepericardial sack, and introducing superfluous fluid into the pericardialsack of a beating heart, all with the attendant risks. If used, itrequires the full surgical suite and delicate and highly skilledsurgical technique. The surgical invasion of the pericardial sack isgenerally not acceptable to practitioners.

Thus, although mild cardiac hypothermia provides protection againstinfarct resulting from a cardiac ischemic event, the existing methods ofachieving cardiac hypothermia are inadequate and unacceptable; a bettermethod of achieving mild hypothermia of the heart that is fast,controlled and less invasive is needed.

SUMMARY OF THE INVENTION

The present invention provides a method for inducing controlledhypothermia of the heart, using an intravascular heat exchange device inthe nature of a catheter. The intravascular heat exchange device isinserted into the vasculature of a mammalian patient and is thereafterutilized to cool blood that is flowing to the patient's heart. In thismanner, hypothermia of the myocardium is achieved. Myocardialhypothermic treatment in accordance with this invention may be useableto prevent or lessen myocardial infarction in patient's who aresuffering from acute myocardial ischemia. Also, the myocardialhypothermic treatment in accordance with this invention may be useableto prevent, deter, minimize or treat other types of damage to themyocardium such as toxic myocardial damage that can occur during orafter administration of certain cardiotoxic drugs or exposure tocardiotoxic agents. Also, the myocardial hypothermic treatment inaccordance with this invention may be useable to prevent, deter,minimize or treat certain cardiac disorders such as cardiac arrhythmiasand the like.

The heart is the body's pump to pump blood throughout the body. A normalheart pumps blood at a rate of 3 liters per minute per square meter andthe average human is 1.7 square meters, so the average heart pumps about5.1 liter of blood per minute for entire life of the person. Undernormal conditions, the blood is maintained at a very constanttemperature of 37° C., and this in turn keeps the heart (and the rest ofthe body) at a very constant temperature of 37° C. The heart temperatureis maintained by both the temperature of the arterial blood and thevenous blood, in addition to the small amount of arterial blood that isre-circulated through the coronary arterial tree to feed the heartmuscle (estimated to be 4% of the total circulation) the average heartpumps about 306 liters of blood per hour, blood that is all circulatedthrough the heart cavities. Therefore cooling the venous blood thatenters the heart will effectively cool the heart by direct contact withthe cardiac muscle in the cardiac cavities.

As may be seen, cooling the venous blood in the vena cava alsoeffectively cools the arterial blood that is circulated through thecardiac arteries. After being cooled in the vena cava, the blood firstenters the right atrium, is then pumped through the lungs (which exposethe blood to air at room temperature which is generally less thannormothermia), from whence it is returned to the left atrium, and thento the left ventricle. The left ventricle pumps the oxygenated blood tothe body through the aorta, and the first arteries to branch off theaorta are the coronary arteries. Thus the blood will be circulatedthrough the arterial tree of the heart without ever having picked upmetabolic heat from the rest of the body. The heart is thus cooled bothby direct contact with the cooled blood and by having the cooled bloodcirculated through the coronary arteries before picking up metabolicheat from the outlying capillary beds.

Described herein is a method for reducing the size of any infarct thatresults from a cardiac ischemic event by inserting a cooling catheterhaving a heat exchange region into the vasculature of a patient, placingthe heat exchange region into the blood stream flowing to the heart,cooling the blood as it passes the heat exchange region and thusdirecting cooled blood to the heart muscle before, during and/or afteran ischemic event for a sufficient length of time to reduce thetemperature of the heart. The method advantageously is practiced byplacing the heat exchange region of the catheter into the patient's venacava, either the inferior vena cava (IVC) or the superior vena cava(SVC), and the heat exchange region may even be placed partially ortotally within the heart itself. The cooling catheter may be introducedinto the patient in any acceptable means, for example percutaneouslythrough the femoral vein into the IVC or via the internal jugular veininto the SVC, by surgical cut-down, or by surgical placement in apatient with an open chest.

The cooling of the cardiac muscle is advantageous if performed after acardiac ischemic event, for example a heart attack, and is advantageousif performed before an anticipated ischemic event, for example before orduring coronary angioplasty or beating heart surgery, and if performedduring an ischemic event, for example during a heart attack in progressor during an angioplasty or beating heart surgery.

The cooling of the blood may be done by a cooling catheter havingvarious acceptable types of cooling regions, for example a coolingcatheter with a balloon for receiving the circulation of heat transferfluid that is cooled outside of the body of the patient. Of particularvalue is the efficiency of a multi-lobed heat exchange balloon. Otherheat exchange elements, however, are also useful in this method. Forexample, flexible metallic heat exchange regions or heat exchangeregions with multiple heat exchange elements would be acceptable forpracticing the patented method.

While the heart may experience some harmful effects of when subjected tovery deep hypothermia such as arrhythmia's at temperatures below 30° C.,profound reduction of infarct resulting from ischemia may be experiencedas a result of mild hypothermia of only a few degrees belownormothermia, for example hypothermia as mild as 35° C. or above,thereby enjoying the benefits of hypothermia while avoiding the harmfuleffects of deep hypothermia. Therefore cooling the heart to mild levelsof hypothermia above 32° C. is preferred in this method. Thesetemperature targets, of course, will vary somewhat from patient topatient, and from circumstance to circumstance.

Beside the level of hypothermia, the time during which the hypothermiais administered may vary according to the circumstances. For example,the heart may be cooled for a short period of time and then rewarmed, ormay be cooled and maintained in a cooled condition for some period oftime. For example, a heart attack victim may have the cardiac musclecooled for an hour, while the hypothermia may be applied during beatingheart surgery for several hours.

The heart may also be selectively cooled. That is, the blood directed tothe heart may be cooled immediately before being directed to the heart,for example, when the blood is in the IVC, and the blood directed to therest of the body after leaving the heart may be warmed, for example by awarming catheter in the descending aorta or warming blankets on the skinof the patient. The method of this invention tends to result in a corebody temperature that is several degrees warmer than the cardiactemperature achieved, at least initially, and this difference can beaccentuated and prolonged by the use of warming blankets or other meansto warm the blood of the patient after the cooled blood has left theheart of the patient.

These and other objects and advantages of the invention can be betterunderstood with reference to the drawings and the detailed descriptionof the embodiments of the invention described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a heat exchange catheter in the vasculature ofa patient with the heat exchange region of the catheter located in thevena cava of the patient.

FIG. 2 is a cross-sectional view of the shaft of a heat exchangecatheter.

FIG. 3 shows a side view of the heat exchange region of a heat exchangecatheter as assembled.

FIG. 4 shows the shaft member of the heat exchange catheter of FIG. 3.

FIG. 5 shows the balloon configuration of the catheter assembly of FIG.3.

FIG. 6 is a view of a portion of the heat exchange catheter of FIG. 3illustrating outflow of heat exchange fluid.

FIG. 7 is a view of a portion of the catheter of FIG. 3 illustratinginflow of exchange fluid.

FIG. 8 is a cross-sectional view of the shaft of FIG. 3 and FIG. 4 takenalong the line 8-8.

FIG. 9 is a cross-sectional view of the balloon of FIG. 5 taken alongthe line 9-9.

FIG. 10 is a cross-sectional view of the catheter of FIG. 3 taken alongthe line 10-10.

FIG. 11 is a cross-sectional view of the catheter of FIG. 3 taken alongthe line 11-11.

FIG. 12 is a cross-sectional view of the catheter of FIG. 3 taken alongthe line 12-12.

FIG. 13 is an illustration of a heat exchange balloon having a spiralshaped heat exchange region in place in the IVC.

FIG. 14 is an illustration of a bellows shaped heat exchange region inplace in the IVC.

FIG. 15 is an illustration of a flexible metal heat transfer region withspiral shaped heat transfer fins and radial heat transfer fins on thesurface of the heat exchange region, said heat exchange region in placein the IVC.

FIG. 16 is an enlarged side view of the heat transfer region of thecatheter of FIG. 15.

FIG. 17 is a cross-sectional view of the heat transfer region of FIG.15.

FIG. 18. is an illustration of a heat exchange catheter having a heatexchange region comprising multiple heat exchange elements in place inthe vena cava.

FIG. 19 is an illustration of a heat exchange catheter inserted into apatient via an internal jugular vein insertion, with the heat exchangeregion in place in the SVC.

FIG. 20 is a graph of the body temperature during cooling as measured atdifferent locations in the body.

FIG. 21 is a flow chart depicting the steps of the method as describedin the detailed description.

DETAILED DESCRIPTION

The present invention comprises a method of cooling the beating heart toprotect myocardial tissue from infarct as a result of ischemia. Theheart is cooled by placing a heat exchange catheter having a heatexchange region in contact with blood flowing to the heart, for example,blood in the IVC, cooling the heat exchange region to a temperaturelower than that of the blood, for example circulating saline at 2° C.through the heat exchange region to cool the heat exchange region toabout 2° C. thereby cooling the blood to a temperature belownormothermia, and maintaining the cooling for a long enough time toreduce the temperature of the heart.

In intravenous cooling such as that described in the previous paragraph,a heat exchange region is placed in the bloodstream and maintained at alower temperature than the blood. The rate of cooling blood by means ofa heat exchange region in contact with flowing blood depends on a numberof factors. One is the difference in temperature between the blood andthe heat exchange region in contact with that blood. Other factorsinclude the specific heat of the blood, the amount of surface area ofthe heat exchange region in contact with the blood, and the heattransfer coefficient between the blood and the surface of the heatexchange region. Certain other factors may also effect the efficiency ofheat transfer between the heat exchange region and the colloidal fluidthat is blood, such as turbulent flow (see e.g. U.S. Pat. No. 5,624,392to Saab, col. 11, II. 56-60) to enhance heat exchange. Where the heatexchange region is cooled by the circulation of heat exchange fluid,counter-current flow between the blood and the heat exchange fluid isimportant so that the heat exchange fluid flows through the heatexchange region in a direction opposite that of the blood flow. In thisway, the warm blood flows over the warmest part of the heat exchangeregion first toward the coldest part of the heat exchange region. It hasbeen found that a balloon heat transfer catheter of the type describedbelow with the heat exchange region placed in contact with blood flowingin the IVC is a satisfactory method of practicing this invention,although other heat exchange catheters with other types of heat exchangeregions are within the scope of the invention.

Essentially all the blood flow into the heart cavities flows through thevena cava, the IVC below the heart and the SVC above the heart. It isestimated that in the ordinary human ⅔ of the total venous return to theheart flows through the IVC and ⅓ through the SVC. The vena cava is alarge vessel; in the human patient, the IVC is generally about 200millimeters long and generally ranges between about 160 millimeters and260 millimeters. In diameter it varies somewhat over that length, butaverages about 21 millimeters in diameter. Cooling blood flowing throughthe vena cava provides an effective way of inducing mild hypothermia tothe heart. Blood flowing through the vena cava is flowing directly tothe heart cavities. It cools the heart directly by contact with theheart muscle. The blood that feeds the cardiac arteries would alsogenerally be relatively cool since blood cooled in the vena cava travelsonly to the lungs before being pumped through the cardiac arteries. Inthe lungs the blood is exposed to air at ambient temperature which isusually below normothermia, and the blood does not travel through therest of the body where it would pick up metabolic heat.

Because large volumes of blood are cooled by the method of theinvention, the temperature of the entire body may be somewhat depressed,that is the patient may experience what is sometimes called whole bodyhypothermia. Although it is generally the case the body functions mostefficiently at normothermia, some whole body hypothermia is acceptableand in some situations may even by therapeutic. In any event, as theexample detailed below describes, the temperature of the body core otherthan the cardiac muscle tends to lag the hypothermia experienced by thecardiac muscle, and this results in even shallower hypothermia than thatexperienced by the cardiac muscle. It is often the case that theapplication of cooling to the heart with the heat exchange region of thecooling catheter in the vena cava tends to be fairly short, perhaps anhour or less, so the core cooling experienced by the whole body whilepracticing this method is generally not harmful.

FIG. 1 shows a heat exchange catheter 10 having a heat exchange region12 located in the IVC 14 of a patient. The heat exchange region ismaintained at a temperature below that of the blood, perhaps as cold as0° C., so that blood flowing past the heat exchange region gives offheat to the heat exchange region and thus is cooled. The cooled blood,indicated by arrows in FIG. 1, flows into the heart 16 and cools theheart.

The balloon heat exchange catheter may be placed in the vasculature of apatient by for example, percutaneously inserting it using the well knownSeldinger technique into the femoral vein 18 and advancing it toward theheart until the heat exchange region 12 is located the vena cava of thepatient. In one preferred method, a balloon heat exchange catheter has aheat exchange region comprising a balloon with mechanisms forcirculating cold saline through the balloon as the heat exchange fluid.The balloon is percutaneously placed into the femoral vein and advancedto locate the heat exchange balloon in the IVC. As shown in FIG. 2, theshaft 18 of the heat exchange catheter has three lumens therein, aninflow lumen 20 for the flow of heat exchange fluid to the heat exchangeregion, an outflow lumen 22 for the flow of heat exchange fluid from theheat exchange region, and a working lumen 24 that may be used for aguide wire or the administration of medicaments from the proximal end ofthe catheter through the distal end of the catheter.

The inflow lumen is in fluid communication with the distal end of theballoon; the outflow lumen is in fluid communication with the proximalend of the balloon. The heat exchange fluid is circulated from outsidethe body, down the inflow lumen to the distal end of the balloon,through the balloon, and back out the outflow lumen. In this examplethis results in the heat exchange fluid flowing in the oppositedirection of the blood, i.e. counter-current flow. This counter-currentheat exchange between flowing liquids is the more efficient means ofexchanging heat.

By controlling the temperature of the saline, the temperature of theballoon may be controlled. The saline may be cooled outside the body by,for instance, an external heat exchanger 26, to cool the saline to aslow as 0° C. The balloon is thereby cooled to as low as 0° C., at leastat the point where the heat exchange fluid first begins to exchange heatwith the blood. As will be readily appreciated, a temperature gradientis established along the length of the balloon. Where the heat exchangefluid first enters the balloon, the balloon is at its coldest. If theheat exchange fluid is at 7° C. for example, when it exits the centrallumen and enters the balloon, the surface of the balloon will beessentially 7° C. At that point if the blood is at normothermic, that is37° C., the DT would be 30° C. and the blood would give off heat throughthe balloon to the heat exchange fluid. It should be noted that not allthe heat exchanged between the blood and the heat exchange fluid will beat the heat exchange region. Some heat may be exchanged between theblood flowing in the femoral vein and the vena cava so the temperatureat the coldest point on the heat exchange region may be as warm as 7° C.even if the saline is cooled by the external cooler to as cold as 0° C.It is preferable to exchange the maximum amount of heat in the IVC nearthe heart by means of the heat exchange region, but the blood in thefemoral vein and IVC which may exchange heat with the shaft of thecatheter ultimately flow past the heat exchange region and into theheart, so that heat exchanged by this portion of the heat exchangecatheter also serves somewhat to cool the heart. Therefore, inevaluating the performance of the catheters used in the preferredembodiments of this invention, the temperature at the inlet to the heatexchange catheter, that is soon after it leaves the external heatexchanger, and the temperature at the outlet of the heat exchangecatheter, that is just before it enters the external heat exchanger, inconjunction with the flow rate of heat exchange fluid in the catheter,can give a useful estimate of the heat exchanged with the blood directedto the heart, although it would include both the heat exchanged at theheat exchange region and heat exchanged along the shaft. For example, inthe multi-lobed heat exchange catheter described in detail below, thetemperature at the inlet may be measured at about 4° C. and thetemperature at the outlet at about 11° C. The flow rate in the cathetermay be about 450 ml/min. This indicated a total heat exchange of about220 watts of energy, a performance adequate for practicing the method ofthis invention.

It should be noted that the exchange of heat from the body may becontrolled by controlling the external heat exchanger. For example, ifmaximum temperature reduction were desired, maximum power to the heatexchange region would result in the coldest possible heat exchange fluidand thus the largest DT between the heat exchange fluid and the blood.Once the target temperature had been reached and the number of wattsneeded to be removed from the blood to maintain the target temperaturewas less, the watts transferred from the body could be reduced byreducing the power to the external heat exchanger. This would in turnincrease the temperature of the heat exchange fluid as it left theexternal heat exchanger and entered the catheter, which would decreasethe DT between the blood and the heat exchange fluid, and thus reducethe watts removed from the bloodstream.

The external heat exchanger may be, for example, a hot/cold plate formedof a number of thermoelectric units such as Peltier units, or other hotor cold elements in contact with a thermal exchange bag through whichthe heat exchange fluid is circulated. If the bag is sealed and forms aclosed circuit with the heat exchange fluid in the catheter, the heatexchange fluid may be heated or cooled exterior of the body without everbeing exposed to the air. If the saline is initially sterile, it maythereby be maintained sterile, an advantage for fluid that is circulatedthrough the body. Although the heat exchange fluid is not intentionallyin contact with the blood, if a leak should occur it would be asignificant advantage to use sterile heat exchange fluid.

The external heat exchange unit, in turn, may controlled by controller28 that may be pre-programmed or may be reactive to a temperature sensor30 that senses the temperature of the patient. As will be readilyappreciated by those of skill in the art, the temperature sensor maysense the temperature of the heart itself to the patient's bodytemperature as measured by a rectal sensor, an esophageal sensor, atympanic sensor or the like. It has been found that the temperaturesensors in the heart tissue when a heat exchange balloon is located inthe vena cava tends to more closely reflect the temperature of the heatexchange balloon than do the rectal, esophageal or tympanic sensors, butthat these various sensors correlate well with each other, and thus,with the appropriate compensation factors, any one of them may be usedto control the temperature of the heat exchange region for purposes ofinducing and controlling cardiac hypothermia.

If the external heat exchanger is able to both heat and cool, as is thecase for example in the Peltier elements described above, the heatexchange fluid may be heated or cooled in response to the signal fromthe sensor. If the external heat exchange unit is able to be controlledas to the amount of heating or cooling it provides, the degree ofheating or cooling supplied by the heat exchange unit may be controlledin response to the signal received from the sensor. As will be seen inthe example described below, this will allow the operator to cool theheart to a predetermined temperature, maintain the heart at apredetermined temperature for a length of time, and add heat to theblood to warm the heart at a chosen point. In practice, the controllerreceives a signal that represents the temperature of the heart tissue.As this temperature nears the target temperature, the controller causesthe external heat exchanger to reduce the amount of cooling applied tothe heat exchanger. By internal calculations, the rate of decrease ofthe temperature of the heart tissue is calculated relative to the amountof energy applied by the external heat exchanger, and as the hearttissue nears and finally reaches the target temperature, the preciseamount of cooling that must be applied by the external heat exchanger tocause a rate of change of essentially 0 is known. By application of thisamount of cooling by the external heat exchanger when the heart reachesthe target temperature, the heart is essentially maintained at preciselythis temperature. In this way, by use of the controller receiving asignal from the patient's body that represents heart temperature, theoperator is able to precisely control the level of hypothermia applied.By determining how long the controller will maintain this level ofhypothermia and when it will begin to re-heat, the length of thehypothermia applied to the heart may also be precisely controlled.

Although the heat exchange region shown in FIG. 1 is a simple, singlelobed balloon, the heat exchange region may be of various advantageousconfigurations. One effective catheter for exchanging heat with theblood in the vena cava is a heat exchange balloon catheter having a heatexchange region that is a multi-lobed balloon and has the temperature ofthe heat exchange region controlled by controlling the temperature ofheat exchange fluid circulated through the balloon.

Such a catheter is depicted in FIG. 3 through FIG. 12. The assembledcatheter 31 (FIG. 3) has a four-lumen, thin-walled balloon 33 (FIG. 5)which is attached over an inner shaft 35 (FIG. 4).

The cross-sectional view of the four-lumen balloon is shown in FIG. 9.The balloon has three outer lumens 37, 39, 41 which are wound around aninner lumen 43 in a helical pattern. All four lumens are thin walledballoons and each outer lumen shares a common thin wall segment 42 withthe inner lumen 43. The balloon is approximately twenty-five centimeterslong, and when installed, both the proximal end 67 and the distal end 89are sealed around the shaft in a fluid tight seal.

The shaft 35 is attached to a hub 47 at its proximal end. The crosssection of the proximal shaft is shown at FIG. 8. The interior of theshaft is configured with three lumens, a guide wire lumen 49, an inflowlumen 51 and an outflow lumen 53. (For purposes of this description theinflow lumen is lumen 51, and the outflow lumen is 53. As one of skillin the art may readily appreciate, the inflow and outflow lumens may bereversed if desired.) At the hub, the guide wire lumen 49 communicateswith a guide wire port 59, the inflow lumen is in fluid communicationwith an inflow port 55, and the outflow lumen is in communication withan outflow port 57. Attached at the hub and surrounding the proximalshaft is a length of strain relief tubing 61 which may be, for example,heat shrink tubing.

Between the strain relief tubing and the proximal end of the balloon,the shaft 35 is extruded with an outer diameter of about 0.118 inches.The internal configuration is as shown in cross-section in FIG. 8.Immediately proximal of the balloon attachment 67, the shaft is neckeddown 63. The outer diameter of the shaft is reduced to about 0.100 to0.110 inches, but the internal configuration with the three lumens ismaintained. Compare, for example, the shaft cross-section of FIG. 8 withthe cross-section of the shaft shown in FIG. 10 and FIG. 11. This lengthof reduced diameter shaft remains at approximately constant diameter ofabout 0.10 to 0.11 inches between the necked down location at 63 and thenecked down location at 77.

At the necked down location 63, a proximal balloon marker band 65 isattached around the shaft. The marker band is a radiopaque material suchas a platinum or gold band or radiopaque paint, and is useful forlocating the proximal end of the balloon by means of fluoroscopy whilethe catheter is within the body of the patient.

At the marker band, all four lobes of the balloon are reduced down andfastened to the inner member 67. This may be accomplished by folding theballoon down around the shaft, placing a sleeve, for example a shortlength of tubing, over the balloon and inserting adhesive, for exampleby wicking the adhesive, around the entire inner circumference of thesleeve. This simultaneously fastens the balloon down around the shaftand creates a fluid tight seal at the proximal end of the balloon.

Distal of this seal, under the balloon, an elongated window 73 is cutthrough the wall of the outflow lumen in the shaft. Along the proximalportion of the balloon, five slits, e.g. 75, are cut into the commonwall between each of the outer balloon lumens and the inner lumen 43.(See FIG. 10 and FIG. 6.) Because the outer lumens are twined about theinner lumen in a helical fashion, each of the outer tubes passes overthe outflow lumen of the inner shaft member at a slightly differentlocation along the length of the inner shaft, and therefore an elongatedwindow 73 is cut into the outflow lumen of the shaft so that each outerlumen has a cut 75 where that lumen passes over the window in the shaft.Additionally, there is sufficient clearance between the outer surface ofthe shaft and the walls of the inner lumen 43 to create sufficient spaceto allow relatively unrestricted flow through the 5 slits 75 in eachouter lumen 37,39,40 to the outflow lumen of the shaft 53.

Distal of the elongated window in the outflow lumen, the inner member 43of the four-lumen balloon is sealed around the shaft in a fluid tightseal 82. The outflow lumen is plugged 79, and the wall to the inflowlumen is removed. (See FIG. 11.) This may be accomplished by neckingdown the shaft 77 to seal the outflow lumen shut 79, removing the wallof the inflow lumen 81, piercing a small hole in the wall of the innerlumen 84 and wicking UV curable adhesive into the hole and around theentire outside of the shaft, and curing the adhesive to create a plug toaffix the wall of the inner lumen of the balloon around the entireoutside of the shaft 83. The adhesive will also act as a plug to preventthe portion of the inner lumen proximal of the plug from being in fluidcommunication with the inner member distal of the plug.

Just distal of the necked down location 77, the guide wire lumen of theshaft may be terminated and joined to a guide wire tube 87. The guidetube then continues to the distal end of the catheter. The inflow lumen81 is open into the inner lumen of the four-lobed balloon and thus influid communication with that lumen.

The distal end of the balloon 89 including all four lumens of theballoon is sealed down around the guide wire tube in a manner similar tothe manner the balloon is sealed at the proximal end around the shaft.This seals all four lumens of the balloon in a fluid tight seal. Justproximal of the seal, four slits slits 91 are cut each the common wallbetween each of the three outer lumens 37, 39, 41 of the balloon and theinner lumen 43 so that each of the outer lumens is in fluidcommunication with the inner lumen. (See FIG. 5 and FIG. 12.)

Just distal of the balloon, near the distal seal, a distal marker band93 is placed around the inner shaft. A flexible length of tube 95 may bejoined onto the distal end of the guide wire tube to provide a flexibletip to the catheter. Alternatively, a soft tip 98 may be attached overthe very distal end of the catheter. The distal end of the flexible tube97 is open so that a guide wire may exit the tip, or medicine orradiographic fluid may be injected distal of the catheter through theguide wire lumen.

In use, the catheter is inserted into the body of a patient so that theballoon is within a blood vessel. Heat exchange fluid is circulated intothe inflow port 55, travels down the inflow lumen 51 and into the innerlumen 43 at the end of the inflow lumen 81. The heat exchange fluidtravels to the distal end of the inner lumen and through the slits 91between the inner lumen 43 and the outer lumens 37, 39, 41.

The heat exchange fluid then travels back through the three outer lumensof the balloon to the proximal end of the balloon. The outer lumens arewound in a helical pattern around the inner lumen. At some point alongthe proximal portion of the shaft, each outer lumen is located over theportion of the shaft having a window to the outflow lumen 76, 74, 73,and the outer balloon lumens have slits 75, 78, 80 that are aligned withthe windows. The heat transfer fluid passes through the slits 75, 78, 80through the windows 73, 74, 76 and into the out flow lumen 53. Fromthere it is circulated out of the catheter through the outflow port 57.At a fluid pressure of 41 pounds per square inch, flow of as much as 500milliliters per minute may be achieved with this design.

Counter-current circulation between the blood and the heat exchangefluid is highly desirable for efficient heat exchange between the bloodand the heat exchange fluid. Thus if the balloon is positioned in avessel where the blood flow is in the direction from proximal toward thedistal end of the catheter, for example if it were placed from thefemoral vein into the ascending vena cava, it is desirable to have theheat exchange fluid in the outer balloon lumens flowing in the directionfrom the distal end toward the proximal end of the catheter. This is thearrangement described above. It is to be readily appreciated, however,that if the balloon were placed so that the blood was flowing along thecatheter in the direction from distal to proximal, for example if thecatheter was placed into the IVC from a jugular insertion, as isillustrated in FIG. 8, it would be desirable to have the heat exchangefluid circulate in the outer balloon lumens from the proximal end to thedistal end. Although in the construction shown this is not optimal andwould result is somewhat less effective circulation, this could beaccomplished by reversing which port is used for inflow direction andwhich for outflow.

As depicted in FIG. 13, a catheter such as that described above, withthe heat exchange region 99 located in the IVC provides an advantageousapparatus for the practice of the method of this invention. Otheradvantageous configurations for the heat exchange region may beemployed, however. For example, the heat exchange region may have abellows-shaped surface 100 as shown in FIG. 6, or the heat exchangeregion 102 may have a surface shaped with alternating right handedspirals 104 and left handed spirals 106 with a bellows shaped surface108 between the spirals as shown in FIGS. 14-17. Another acceptablevariation of the heat exchange catheter would have a heat exchangeregion 110 comprising multiple heat exchange elements 112 as illustratedin FIG. 18.

Those of skill in the art will also readily appreciate that, beside theuse of different heat exchange regions, other acceptable placements ofthe heat exchange region may be employed to practice the method of thisinvention. For example, An internal jugular insertion may be madewherein the catheter is inserted into the internal jugular vein 120 andthe heat exchange region advanced to, for example, the SVC 122 asillustrated in FIG. 8. With an internal jugular insertion, if the heatexchange region is only advanced into the SVC, the blood flow will befrom the proximal to the distal end of the heat exchange region, i.e. inthe same relative direction as with a femoral insertion and placement ofthe heat exchange region in the IVC, so counter-current flow between theheat exchange fluid and the blood will be maintained with the samecatheter as described above.

EXAMPLE

The method of the invention may be described by reference to thefollowing example. In the instance described here, the cardiac coolingmethod of the invention was performed using 60 B 80 kg. pigs. The studywas conducted in accordance with The Guide for Care and Use ofLaboratory Animals. Each pig was anesthetized with isoflouraneanesthesia, and vascular sheaths were inserted percutaneoulsy in to thefemoral artery and vein respectively. A median sternotomy was done,followed by the isolation of the left anterior descending coronaryartery. A three lobed heat exchange catheter as described above wasinserted into the sheath in the femoral vein and the catheter wasadvanced until the heat exchange region was in the IVC just below theheart. Saline was circulated through the heat exchange region of thecatheter and an exterior heat exchanger. The exterior heat exchanger wasin the form of a hot/cold plates formed by a number of Peltier units,and a bag of saline in contact with the plates. The circuit of thesaline through the bag and through the catheter including the heatexchange region was closed, and the saline was sterile. The temperatureof the Peltier plates, and thus of the saline, was controlled by alap-top computer using a commercially available control program readilyavailable to and understood by those of skill in the art, and wascontrolled in response to core temperature sensed by an esophagealtemperature sensor of the type typically used in the medical arts.

The core temperature was initially maintained at 38° C. (normothermiafor pigs) by adding or removing heat as necessary with the heat exchangecatheter. Because the chest had been opened by the sternotomy, thisgenerally comprised adding a small amount of heat to the blood. The leftanterior descending coronary artery was occluded for a total of 60minutes about 213 of the way down its length using a snare. The snarewas formed using a suture placed around the descending coronary artery,with both legs of the suture contained within a plastic tube. The snarewas tightened and the occlusion formed by sliding the tube down againstthe artery.

Twenty minutes into the occlusion, the external heat exchanger wasturned on with the controller was set to remove heat via the heatexchange catheter to lower the cardiac temperature of the pig at themaximum rate. Heat was removed from the blood flowing through the IVC ata rate that varied somewhat between test animals from about 140 watts to220 watts, but was generally about 190 watts.

At the end of the 60-minute period of ischemia, the snare was loosenedby removing the plastic tube by sliding it away from the artery and offthe suture. The removal of the snare restored flow to (re-perfused) theischemic area. The suture was left, lose but in place around the artery.Cooling in order to maintain the target temperature of 34° C. wasmaintained for 15 minutes after the removal of the occlusion. In thepigs receiving hypothermia, there was thus a total of 55 minutes ofcooling: beginning after 20 minutes of occlusion; 40 minutes of coolingduring occlusion; then 15 more minutes of cooling after re-perfusion.

After the period of cooling (55 minutes) the external heat exchanger wasswitched to begin heating, and the temperature of the saline circulatingthrough the heat exchange catheter was raised to 41° C. This in turnbegan warming the blood and rewarming the pig toward normothermia.

The control pigs were maintained at normothermia (38° C.) initially andduring occlusion, and this temperature was maintained for an additionalthree hours after reperfusion. In the hypothermic pigs, re-warmingtoward 38° C. was allowed to occur for 2 hours and 45 minutes, that isalso until three hours after reperfusion. At the end of this period (4hours after the initial occlusion), the suture was again tied off aroundthe artery to occlude the vessel, and monastral blue dye was injectedinto the left ventricular cavity to define the ischemic area at risk.The dye stained all the areas of the heart that were vascularized, andsince the suture was tied off around the cardiac artery at the samelocation as originally occluded, the area at risk would be unstained andwould visually accurately define the area at risk during the originalischemia.

The heart was harvested to analyze the effect of the hypothermia oninfarct resulting from the ischemic event. The heart was excised, slicedinto 0.5 to 1.0 cm slices, and the slices were immersed into 1%triphenyltetrazolium chloride (TTC) for 15 minutes to stain the viabletissue. Nonviable tissue is not stained by TTC. The myocardial sliceswere photographed using a digital camera and the area at risk, and theinfarction zones were quantified using image analysis software. Sixanimals were studied with hypothermia, while an additional six animalsserved as controls. For the controls, the heat exchange catheter wasplaced into the IVC and the controller set to maintain the esophagealtemperature 38° C. Otherwise, the procedure was identical for theexperimental hypothermia animals and the controls. Results below areexpressed as 1) Area at risk (AAR), and 2) Percent of AAR that sufferedinfarct.

Results:

HYPOTHERMIC CONTROL AAR IF/AAR AAR IF/AAR Pig # (% LV) (% AAR) Pig # (%LV) (% AAR) 1 11.3 0.0 1 25.4 49.1 2 13.6 0.0 2 12.6 35.9 3 11.2 0.0 314.9 44.8 4 21.1 0.8 4 33.6 45.1 5 18.2 0.0 5 17.7 61.5 6 23.7 12.8 610.4 47.0 Mean ± 16.6 ± 5.3 2.3 ± 5.3 Mean ± 19.1 ± 8.8 47.2 ± 8.3 SD SDP Value P = NS P < 0.000005 Hypother- mic vs. Normo- thermic

It should be noted that the core temperature of the pig as measured bythe tympanic or rectal probe never reached as low a temperature as didthe heart itself. A graph showing the temperatures as measured atdifferent locations during one experiment is depicted in FIG. 20. Thecardiac temperature was measured by temperature sensors located in themuscle of the left ventricle and of the left atrium. Temperatures werealso measured by sensors in the rectum, in the eardrum (tympanic) and inthe esophagus. All of the temperatures measured away from the heartitself tended to lag the cardiac temperature, sometimes as much as 2° C.Presumably the fact that the heart was contacted with the cool bloodfirst, and even warmed that blood somewhat before it went out to otherlocations would explain this difference.

If the heart had reached a target temperature, and the rate of coolinghad been reduced to only that necessary to maintain that targettemperature, the rate at which the rest of the body would haveapproached equilibrium would have slowed considerably, and the core bodytemperature as measured away from the heart would have continued to lag.Presumably, however the body would ultimately reach equilibrium at somehypothermic temperature.

This, however, would take a long time, and in the time while the heatexchange catheter was cooling the heart at hypothermic temperature, thebody temperatures never reached equilibrium. Once the heat exchangecatheter began to warm the blood, the entire body began to experiencewarming, and therefore the body core away from the heart neverexperienced hypothermia as deep as that experienced by the heart. Forthe times involved in the hypothermic treatment of the method, and forthe depth of hypothermia involved, the whole body cooling that resultedwas within acceptable limits.

In humans, the same method of applying hypothermia can be used to reduceinfarct resulting from an ischemic event. A multi-lobed balloon cathetersuch as that described above, may be percutaneously placed through thefemoral vein so that the heat exchange region is located in the IVC orthrough the internal jugular vein so that the heat exchange region islocated in the SVC, and the blood therein cooled by cooling the heatexchange region (the balloon) by circulating cold saline through thecooling catheter. Saline at about 0° C. can be circulated without unduedamage to the blood. A controller receiving a signal representingcardiac temperature, either directly or through some surrogate such asesophageal or tympanic temperature, can control the heat exchangecatheter to achieve a target temperature and maintain that temperature.As was the case with the pigs, the heat removed from the blood alsoresults in overall temperature reduction in the whole body since thebody is unable to generate sufficient heat to replace that amountremoved by the heat exchange catheter, but the heart tends to cool morerapidly than that of the rest of the body. The whole body cooling may bedesirable in some instances for therapeutic reasons, for example forneuroprotection is some global ischemia is experienced, but at least atthe mild levels of hypothermia in the method of the invention, and forthe time lengths expected, therapeutic hypothermia of the heart isobtained by this technique without undue injury to the patient. It isanticipated that means to inhibit shivering using drugs such asmeperidine, Thorazine, Demerol, phenegran or combinations thereof, orapplying heat to the skin surface may be necessary to prevent or reduceshivering in unanesthesized patients receiving hypothermic therapy.

The method of the invention is described in the flow chart of FIG. 21.In Step 1, the heat exchange catheter is inserted into the vasculatureof a patient. This is typically inserted percutaneously into the femoralvein, but may also be inserted into the internal jugular vein, or in anyother suitable fashion depending on the circumstances. For example, ifthe patient is in surgery, insertion by a cut-down may be preferable. Ifaccess to the listed veins is not possible because the patient is agedor has other catheters or the like occupying the preferred locations,alternative locations are within the scope of the invention. Use of aninsertion diameter of 8 French or less (3 F/mm) is generally preferable,but larger catheters are within the anticipated scope of the invention.Use of any of the cooling catheters described above is anticipated, aswould be the use of any acceptable intravenous cooling catheter.

In step two, the catheter is advanced until the heat exchange region isin the blood stream flowing to the heart. This catheter placement iseasily accomplished by those of skill in the art. It may be advancedusing a guide wire, without a guide wire, using a guide catheter, orwithout a guiding catheter. It may be advanced using other well-knowntechniques as appropriate for the situation and the structure of thecatheter, for example using bare wire or rapid exchange technique ifapplicable. It may be advanced from the femoral vein into the IVC, froman internal jugular insertion into the internal jugular vein into theSVC or the IVC, or if appropriate, even into the heart itself fromeither femoral or internal jugular insertion. Any location for theinsertion and placement of the catheter that results in cooling of theblood directed to the heart is within the anticipated scope of thisdisclosure.

In step three, the heat exchange region is cooled below the temperatureof the blood. The heat exchange region may be cooled to about 0° C.,although it should not be cooled much below that temperature. The bloodis largely water and is generally not damaged by contact with a surfacethat is as cold as 0° C. for the length of time that the blood is incontact with the heat exchange region, but with a surface much colderthan that, blood in contact with the heat exchange region would freeze,possibly damaging the blood and decreasing the effectiveness of heatexchange. However, cooling below that temperature might be acceptable ifan acceptable, safe and efficient method of cooling were employed, aslong as it resulted in the cooling of the heart by means of cooling ofthe blood directed to the heart to reduce infarct suffered as a resultof an ischemic event. The method described in greatest detail above ofreducing the temperature of the heat exchange region was circulatingcold saline through a balloon or hollow metallic element, or multipleheat exchange elements, to exchange heat with the blood through thesurface of the heat exchange element, but other acceptable means ofcooling the heat exchange region may be employed in practicing thisinvention.

The fourth step of the invention involves maintaining the exchanging ofheat for a sufficient length of time to reduce the temperature of theheart. In the examples shown, about 240 watts of heat were being removedfrom the blood in the IVC to lower the temperature of the heart from 38°C. to about 33° C. in about 55 minutes. Depending on the desired levelof hypothermia, the amount of blood flowing past the catheter, thenumber of watts of heat being removed from the blood by the heatexchange region, and similar variables, that rate of cooling may well bedifferent and still be within the scope of this invention. It isgenerally the case that the cardiac temperature will be lowered to 35°C. or less to enjoy the benefits of mild hypothermia to reduce infarct,but depending on the individual situation, this may vary somewhat andstill fall within the scope of this invention.

The application of hypothermia may be before the ischemic event, if anischemic event is anticipated as is the case in surgery when it is knownthat the heart will be stopped for some period of time, or duringballoon angioplasty when it is known that areas of the heart downstreamof the balloon will be deprived of blood for some period of time. Thehypothermia may be applied during the ischemia, as when it is appliedduring the two situations described above, whether or not it was appliedbefore the ischemic event, or when it is applied to a heart attackvictim when that victim presents. It may be applied after the ischemicevent has occurred, as when it is applied to a heart attack victim soonafter the ischemic event has occurred but after the ischemia hasresolved and reperfusion has occurred. In all these cases and incombinations thereof, the application of mild hypothermia will generallybe beneficial to prevent infarct from resulting from the ischemic event.

Step 5 involves controlling the heat exchange region in response toheart temperature. This generally involves monitoring a temperature suchas rectal, tympanic, esophageal, cardiac or other temperature that maybe used to determine the temperature of the heart, and controlling theheat exchange region in response to that measurement. The control of theheat exchange region may be in many forms. One form described in detailabove was the control of the temperature of heat exchange fluid beingcirculated through a heat exchange balloon that comprised the heatexchange region. This could be done, for example, by controlling thetemperature of an external heat exchanger that was in contact with a bagof saline, which saline was being circulated through the heat exchangeballoon. However, if the heart temperature is determined by otherfactors, such as the length of time of cooling, the amount of heattransfer, or other physiological measurements, the control may beexercised based on these features.

The specific activities that may constitute control are many. Coolingmay be stopped and heat added to the blood after the heart has reached acertain target temperature. Alternatively, the heat exchange region maybe removed, or the heat exchange region may be returned to normothermia.In a more elegant type of control, a target temperature may bepre-selected and the amount of heat added or removed from the blood maybe adjusted so that the cardiac temperature achieves the targettemperature and stays at the target temperature for some pre-selectedlength of time, and then may warm or cool toward a second pre-selectedtemperature that may be normothermia, or the like. The nature of thecontrol in response to the temperature of the heart may vary greatly andstill be within the scope of this invention.

Step six, optional but sometimes a step practiced in the method, is toadd heat to the hypothermic heart.

Although several illustrative examples of means for practicing theinvention are described above, these examples are by no means exhaustiveof all possible means for practicing the invention. The scope of theinvention should therefore be determined with reference to the appendedclaims, along with the full range of equivalents to which those clamsare entitled.

What is claimed is:
 1. A method for deterring myocardial damage in apatient who is suffering from a heart attack, said method comprising thesteps of: (A) inserting a heat exchange catheter having a heat exchangerwith a helical heat exchange surface into the vena cava of the patient;(B) circulating cooled heat exchange fluid through the heat exchanger tolower the patient's body temperature to 35 degrees C. or below; and,thereafter, (C) performing a procedure to restore blood flow to anischemic area of the patient's myocardium; and, thereafter; (D)rewarming the patient's body to normothermia; wherein heat exchangefluid flows through the heat exchanger in a direction that is oppositethe direction in which blood flows past the heat exchanger.
 2. A methodaccording to claim 1 wherein the helical heat exchange surface compriseshelical fin formed on the heat exchanger.
 3. A method according to claim1 wherein the helical heat exchange surface comprises a helical heatexchange balloon.
 4. A method according to claim 1 wherein the patient'sbody temperature is determined by placement of a temperature sensor inthe patient's body.
 5. A method according to claim 4 wherein thetemperature sensor is placed in the patient's rectum.
 6. A methodaccording to claim 4 wherein the temperature sensor is placed in thepatient's esophagus.
 7. A method according to claim 4 wherein thetemperature sensor is placed in the patient's ear to sense temperatureat the tympanic membrane.
 8. A method according to claim 4 wherein thetemperature sensor is placed in the patient's heart.
 9. A methodaccording to claim 8 wherein the temperature sensor is placed in theleft atrium of the patient's heart.
 10. A method according to claim 8wherein the temperature sensor is placed in the left ventricle of thepatient's heat.
 11. A method according to claim 4 wherein thetemperature sensor is located on the heat exchange catheter.
 12. Amethod according to claim 1 wherein the procedure comprises anangioplasty procedure.
 13. A method according to claim 1 wherein theprocedure comprises a stenting procedure.
 14. A method according toclaim 1 wherein the procedure comprises cardiac surgery.
 15. A methodfor deterring myocardial damage in a patient who is suffering from aheart attack, said method comprising the steps of: (A) inserting a heatexchange catheter having a heat exchanger with a helical heat exchangesurface into the vena cava of the patient; (B) circulating cooled heatexchange fluid through the heat exchanger to lower the patient's bodytemperature to 35 degrees C. or below; and, thereafter, (C) performing aprocedure to restore blood flow to an ischemic area of the patient'smyocardium; and, thereafter; (D) rewarming the patient's body tonormothermia; wherein a temperature sensor is placed in the patient'sheart.
 16. A method according to claim 15 wherein the temperature sensoris placed in the left atrium of the patient's heart.
 17. A methodaccording to claim 15 wherein the temperature sensor is placed in theleft ventricle of the patient's heat.
 18. A method according to claim 17wherein the temperature sensor is located on the heat exchange catheter.19. A method according to claim 15 wherein the procedure comprises anangioplasty procedure.
 20. A method according to claim 15 wherein theprocedure comprises a stenting procedure.
 21. A method according toclaim 15 wherein the procedure comprises cardiac surgery.
 22. A methodaccording to claim 15 wherein heat exchange fluid flows through the heatexchanger in a direction that is opposite the direction in which bloodflows past the heat exchanger.
 23. A method according to claim 15wherein the helical heat exchange surface comprises a helical finsformed on the heat exchanger.
 24. A method according to claim 15 whereinthe helical heat exchange surface comprises a helical heat exchangeballoon.